(57) In a coprocessor system having a central processing unit (CPU, 100) as a host processor,
a floating-point processing unit (FPU, 101) as a coprocessor and a memory (RAM, 103),
coupled with each other through buses (104-106), when the CPU issues a save command
to the FPU (101), the FPU (101) discriminates the attribute, i.e., a long command
or a short command, of a current command executed by the FPU (101) upon receipt of
the save command and the internal status thereof. In response to the discrimination
result, the FPU (101) interrupts the execution of the current command at once to start
the execution of the received save command, when the current command is a long command,
and the FPU (101) executes the received save command after the completion of execution
of the current command, if the current command is a short command. The attribute of
a command is determined in advance on the basis of a time necessary for executing
the command and a predetermined criterion provided therefore.
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